Rod compensator for subsurface well pumps



Feb. 6, 1968 T. L. CROWE ROD coMPENsAToR FOR SUBSURFACE WELL PUMPS 4 Sheets-Sheet l Filed April 29, 1966 T. l.. cRowE Ron coMPENsAToR Foa sUBsURFAoE WELL PUMPS Filed April 29, 195e Feb. 6, 1968 4 Sheets-Sheet 2 Y INVENTOR fi: l

Feb. 6, 1968 T. L. cRowE ROD COMPENSATOR FOR SUBSURF'ACE WELL PUMPS 4 sheets-sheet 3 lfra. 5a.

Filed April 29, 1966 INVENTOR ZL M9065 L. Ceows Feb. l6, 1968 T. cRowE I ROD CONIPENSTOR FOR SUBSURFACE WELL PUMPS 4 Sheets-Sheet 4 Filed April 29, 1966 l INVENTOR #rma/594s.

IJLMQ@ 6E L. Ceowe United States Patent C) M 3,367,279 ROD COMPENSATR FOR SUBSURFACE WELL PUMPS Talmadge L. Crowe, Houston, Tex., assigner to Baker Oil Tools, Inc., Commerce, Calif., a corporation of California Filed Apr. 29, 1966, Ser. No. 546,352 Claims. (Cl. 10S-202) The present invention relates to subsurface well pumps, and more particularly to devices for insuring the proper length of stroke or travel of a pump plunger in its companion barrel.

In a deep well pump operated by a string of reciprocating sucker rods, the etiiciency of the pump is oftentimes comparatively low because of the inability of the travelling valve of the pump to shift downwardly toward the standing valve of the pump to a sutcient extent. Preferably, the travelling valve should move on its downstroke to an extent in which it is disposed closely adjacent to the standing valve of the pump. Such close spacing is not obtained in many cases for a variety of reasons, including improper initial spacing between the travelling and standing valves, upon assembly of the pumping apparatus, or variations in the spacing between the travelling valve and standing valve caused by changes in uid levels in the well, the temperature of the fluids in the well, and in the density of the fluids being pumped. The incomplete or insui'licient lowering of the travelling valve on its downstroke results in reduction in efficiency, ranging from complete inability to pump the tluid caused by trapping of gas between the travelling and standing valves (a gas lock condition) to no loss in eticiency whatsoever, which would occur where the pump barrel lls completely with an incompressible fluid of consistent density, a condition occurring rarely in oil and gas well operations.

When pumping a compressible fluid, a portion of the downstroke is consumed in compressing a tluid below the travelling valve to a pressure somewhat greater than the hydrostatic pressure of the column of fluid in the tubing above the travelling valve. At this point, the travelling valve will open and fluid previously trapped or contained between the travelling valve and standing valve will be transferred relatively upwardly through the travelling valve for the remainder of the downstroke. lt is evident that the amount of downstroke consumed before the travelling valve opens can vary considerably, since it depends on the hydrostatic pressure, the pump intake pressure, low restriction, and the compressibility of the fluids entering the pump. It is only after the travelling valve opens that effective work can be performed. Accordingly, to obtain maximum possible pump volumetric emciency, it is necessary that the unswept volume of the pump be held to a minimum; that is, at the bottom of its stroke the travelling valve should be as close to contacting or bottoming out on the standing valve cage as is practical.

To avoid the above-noted difliculties, the suckerrod string can -be adjusted in length to cause the travelling valve or pump plunger to actually pound against the barrel at the bottom of each stroke. This procedure may produce a high volumetric efliciency, but it normally occasions premature fatigue failure of the pumping system in general and of the rod string in particular, producing high and sometimes prohibitive operating expenses.

Accordingly, it is an object of the present invention to provide an improved apparatus that insures the positioning of a travelling valve closely adjacent to the standing valve of a pump at the bottom of the travelling valve stroke, regardless of, the prior absence of such close positioning between the parts.

Another object of the invention is to provide an ap- 3,367,279 Patented Feb. 6, 1968 ICC paratus for automatically and mechanically changing the length of a sticker rod string to the extent required to insure positioning of the travelling valve of a pump closely adjacent to the standing valve of the pump at the bottom of the travelling valve. In fact, the effective length of the sticker rod string may be changed to an extent producing light contact or tapping of the travelling valve or part connected to it against a stationary pump part at the bottom of each 'stroke of the travelling Valve.

A further object of the invention is to provide a sucker rod compensator that automatically adjusts and corrects the length of the overall sucker rod string in response to rotary movement of the rod string to secure maximum eiiiciency of the pump in the well bore reciprocated by the rod string. A full pump stroke is assured for maximum volumetric eiciency and the elimination of gas lock, despite changes in well conditions that tend to alter the effective length of the rod string.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration ot a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specication. It will now be described in detail, for purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best delined by the appended claims.

Referring to the drawings:

FIGURE 1 is a diagrammatic View of a well pumping system embodying the invention;

FIG. 2 is a longitudinal section through a sucker rod rotator shown in FIG. l;

FIG. 3 is a section taken along the line 3 3 on FIG. 2;

FIGS. 4, 4a and 4b together constitute a longitudinal section through a rod compensator device used in the system disclosed in FIG. l, FiGS. 4a and 4b being lower continuations of FIGS. 4 and 4a, respectively;

FlGS. 5 and 5a together constitute a somewhat diagrammatic section through a combination of the rod compensator of FlGS. 4, 4a, 4b and a reciprocating pump therebelow, FIG. 5a being a lower continuation of FIG. 5;

FIGS. 6 and 6a are views similar to FIGS. 5 and 5a, with parts in another relative position;

FIG. 7 is a cross-section taken along the line 7 7 of FiG. 4a.

As disclosed in the drawings, a string of tubing A is disposed in a well bore B and has a known type of deep well pump C therewithin. The particular pump illustrated by way of example includes a barrel 10 suitably secured or anchored in the tubing string, and a plunger 11 reciprocable in the barrel through upward and downward movement of a sucker rod string 12 connected thereto. As is well known, this sucker rod string may be connected to a suitable mechanism D for effecting its reciprocation, such as a walking beam, hydraulic pumping mechanism, or the like. The outer barrel 10 of the pump has a standing valve mechanism therein, including a valve seat 13 through which wellbore -fluid can ow upwardly into the barrel, downward tlow of the fluid from the barrel being prevented by a valve element 14 adapted to move downwardly into engagement with the seat. The pump plunger is movable upwardly and downwardly in the barrel, containing a travelling valve mechanism in the form of a ball valve element 15 adapted to shift downwardly into engagement with its companion seat 16 surrounding the inlet 17 to the plunger. During the downstroke of the plunger, its travelling valve 15, 16 moves downwardly toward the standing valve 13, 14, the latter closing and the uid thereabove passing through the seat 16 of the travelling valve, unseating its valve element in an upward direction, and then passing upwardly through openings in a plunger partition 21 to a position thereabove. When the plunger 11 is moved upwardly, its valve element 15 engages its seat 16, causing the plunger to lift the entire fluid column in the tubing string A and discharge a portion of it at the top of the well bore. The fluid in the plunger itself can pass through its upper ports 22 into the barrel 10 thereabove and through the upper ports 23 in the guide portion 24 of the barrel through which the plunger rod 25 is reciprocable. During upward movement of the plunger 11, its travelling valve 15, 16 moves upwardly away from the standing valve 13, 14, the valve element 14 of the latter moving off its seat 13 and allowing well bore fluid to flow upwardly through the seat 13 and through openings 18 in a barrel partition 19 into the barrel.

For maximum volumetric efficiency, it is desirable for the plunger 11 to move on its downstroke to a position in which its travelling valve 15, 16 is closely adjacent to the standing valve 13, 14 of the barrel. Accordingly, on the upstroke the plunger 11 will partake of a maximum effective travel in the barrel 10 and will lift a maximum quantity of fluid that may have passed through the travelling valve into the plunger and outer barrel thereabove. lf the uids contain a substantial quantity of gas, assurance is had that the gas between the travelling and standing valves 15, 16 and 13, 14 will be compressed sufciently on the downstroke of the plunger to overcome the hydrostatic head of fluid in the tubing string A, for the purpose of unseating the travelling valve element 15 and causing the fluid above the standing valve 14, 13, including the gas therein, to travel upwardly into and through the plunger 11. lf the travelling valve 15, 16 does not move downwardly to its maximum extent, then gas locking might occur under some conditions, in which the travelling valve does not open on its downstroke, the plunger 11 on its upstroke merely allowing the trapped gas to expand, the standing valve element 14 also remaining in its closed condition with no additional uid from the well bore flowing past it and into the pump barrel 10.

To offer assurance that the plunger 11 and its travelling valve 15, 16 will shift downwardly to the desired maximum extent, an automatically adjustable compensator 27 is included in the sucker rod string 12, as between the plunger rod 25 and a sucker rod section 2S. The plunger rod 25 is preferably secured to a suitable length of polished rod 29, which, for example, may be 30 feet long, and this polished rod is attached directly, or through a short pony rod (not shown), to the threaded pin 30 of a lower sub 31 constituting a portion of the compensator apparatus 27. The threaded pin 32 of an upper sub or housing member 33 of a housing portion 50 of the compensator apparatus 27 is secured to the sucker rod section 28, the sucker rods 12 extending to the top of the hole B. The top sub is threadedly secured to an upper housing section 34, the lower end of which is threadedly attached to a lower housing section 35 threadedly connected to a bottom housing sub 36 that may have axial lugs or clutch elements 37 formed therein, for the purpose of meshing with companion dog clutch elements 38 projecting upwardly from the lower sub 31. This lower sub 31 is threadedly secured to the lower end of an elongate mandrel 40 extending upwardly in the housing 50 and having an upper guide head 41 for sliding along the inner wall of the upper housing section 34, the mandrel being telescopically related to the surrounding housing.

Longitudinal movement between the housing 5() and mandrel 40 is transmitted through a lock or latch device 42 disposed therebetween. As shown, the mandrel has a left-hand thread 43 of a substantial longitudinal extent, which is preferably of left-hand, and which may actually be a buttress thread facing in a downward direction. This external thread 43 meshes with a companion internal thread 44 on a plurality of latch dogs 45 formed at the lower portion of a lock or latch sleeve 46 disposed between the mandrel 40 and lower housing section 35. The latch sleeve is provided with a plurality of circumferentially spaced, longitudinal slots 47 opening downwardly through the lower ends of the dogs and providing exible spring-like legs 4S that will permit a ratcheting action to occur between the dogs 45 and the mandrel. Specically, the mandrel 40 can shift upwardly within the dogs, the latter expanding outwardly and then snapping back into mesh with the mandrel teeth 43.

The outer surfaces 49 of the lock or latch dogs taper in a downward and inward direction, engaging a companion tapered surface 51 on a cam member 52 disposed in the annular space 53 between the mandrel and housing. Upward motion of the housing structure 50 is transferred to the cam member 52 through a strong spring 54, such as a conical spring, consisting of a plurality of stacked Belleville washers, the lower end of which engages the upper end 55 of the bottom housing sub 36, and the upper end of which engages the cam 52. When the clutch` 37, 38 is engaged, an upward stroke of the sucker rods 12 and housing 50 will first compress the spring 54 sutiiciently to allow the clutch teeth 37 of the housing sub to move upwardly out of engagement with the clutch teeth 38 on the bottom sub of the mandrel, after which the upward motion is transmitted through the cam 52 and lock dogs 45 and the intermeshing internal and external threads 44, 43 to the mandrel 40, elevating the mandrel and the pump plunger 11 connected thereto in order to elevate the fluid in the tubing string A. On the downstroke of the sucker rods, the housing structure 5i) moves downwardly, the mandrel 40, rod 29 and plunger 11 connected thereto having sufficient weight as to shift downwardly as a unit with the housing structure 50, the lock sleeve 46, cam 52 and Belleville springs 54 moving downwardly as a unit with the mandrel and the surrounding housing structure.

The lock sleeve 46 is urged in a downward direction to maintain its dogs 45 releasably wedged between the cam 52 and the mandrel 4i) by a helical compression spring 57 disposed between the mandrel and lower housing section, the lower end of the spring engaging the upper end of the sleeve 46, and the upper end of the spring engaging an inwardly directed liange or spring seat 58 integral with the lower housing section 35. The spring 57 will yield sufficiently in the event of relative upward shifting of the mandrel 4() in the housing 50 to allow the dogs 45 to shift upwardly relative Ito the cam 52 and thereby permit them to be forced outwardly by the left-hand threaded ratchet thread 43 on the mandrel out of mesh with such thread, permitting the mandrel to move upwardly within the dogs. However, upward movement of the cam 52 and dogs 45, or relative downward movement of the mandrel 49, will effect a wedging of the dogs between the cam and the mandrel and will lock the mandrel to the housing 50 for longitudinal movement therewith.

The overall length of the rod compensator 27 can be varied, and such length increased in response to movement of the sucker rod string 12. On each upstroke of the sucker rod string and the compensator device, a small turning motion is imparted to the sucker rod string 12, which rotary motion will also rotate the housing 50. This rotary motion is transmitted to the latch sleeve 46 and its dogs 45 by a plurality of circumferentially spaced keys 60 which fits slidably in longitudinal keyways 61 in the lower housing section, and which also extend between the dogs 45 (FIG. 7). These keys are received within grooves 62 in the cam 52 and are suitably secured thereto, as by brazing. The turning motion of the housing 50, as to the right, will also turn the dogs 45 to the right, and, in view of their left-hand threaded engagement with the mandrel 40, will feed the mandrel relatively downwardly with respect to the dogs and with respect to the surrounding housing structure 50, thereby increasing the overall length of the rod compensator. In order to secure the relative rotation of the dogs 45 around the mandrel 40, the latter is prevented from rotating. As specifically disclosed, its rotation is prevented by slidably splining the plunger rod 25 to the guide 24, as by making the plunger rod of square cross-section and having it slide within a companion square-shaped axial passage in the guide. Since the square plunger rod 25 is connected to the mandrel 50 through the intervening polished rod 29 and Vbottom sub 31, the mandrel is prevented from rotating.

On each upstroke of the sucker rod string 12, compensator 27, and pump plunger 11, lthe sucker rod is given a partial rotation through use of a known mechanism 70 at the top of the hole. As shown in the drawings by way of example, a rod rotator 70 is mounted on the usual polished rod 71 at the upper end of the string of sucker rods 12. The walking beam 72 is connected, in a known manner, to the polished rod 71 by securing the lower ends of a pair of short lpieces 73 of cable, attached to the walking beam, to a supporting head 74 through which the polished rod 71 extends. The rod rotator 7l) rests upon this head, the upper pillar post and cover cap 75 of the rod rotator being suitably secured to a rod clamp 76 therea-bove, of a known type, fixed to the polished rod in a known manner, as by the slips 77. As disclosed in FIGS. 2 and 3, the rod rotator includes a body 78 having an upwardly extending inner skirt 79 which is surrounded by a depending skirt portion 88 of the pillar post and cover cap 75, the latter being suitably secured to a ratchet table 81 having upwardly facing ratchet teeth 82 thereon. The ratchet table 81 rests upon a bearing device 83, which, in turn, is supported by the lower wall 84 of the body 78. Rotatably mounted in the body is a crankshaft 85 having a crank pin 8o connected to an actuator pawl 87, the free end 88 of which is adapted to engage the ratchet table teeth 82 so as to turn the ratchet table 81 and the pillar post and cover cap 75 secured thereto in a right-hand direction on each power stroke of the power pawl. Such rotary motion is transmitted through the polished rod clamp 76 to the polished rod 71 and the string of sucker rods 12 connected thereto. The crankshaft 85 is turned in opposite directions by an actua-tor lever 89 secured thereto. The free end of this lever is attached to a cable 11, which is, in turn, attached to some stationary portion, such as the framework 91 supporting the walking beam. As the walking beam 72 elevates the polished rod 71 and the string of sucker rods 12 and rod compensator 27 connected thereto, the cable 98 exerts a pull on the lever against the force of a tension spring 95 interconnecting the lever and walking beam to shift the lever in a direction in which the power or actuator pawl 87 engages the ratchet table 81 and turns it a fraction of a revolution, this rotary motion being transmitted through the string of sticker rods 12 to the housing structure 50, and through the keys 6i) to the lock dogs 45, to rotate the latter around the mandrel 40 and effect a relative upward feeding of the dogs 45 and the housing structure 50 with respect to the mandrel. During such upward stroke, the housing 5t) is shifted upwardly sufliciently to insure the disengagement of the clutch 37, 38, the Belleville spring washers 54 being compressed. Upon downward movemen-t of the polished rod 71 and sucker rods 12, the actuator lever 89 is moved in the opposite direction by the spring 95, its power pawl moving freely over the table teeth 82. However, return movement of the ratchet table 81 is prevented by a holding pawl 96 pivotally connected to the body 78 of the rod rotator and engageable with the teeth of the ratchet table. Thus, reciprocation of the polished rod 71 and the string of sucker rods 12 is accompanied by a step-bystep turning of the string of sucker rods 12, the housing 50 of the rod compensator, and of the latch sleeve 4o around the mandrel 40, effecting a step-by-step relative upward feeding or threading of the housing section 5i) along the mandrel 411 to increase the overall length of the rod compensator 27.

The pump assembly C is connected to the lower polished rod 29, the latter being connected to the lower sub 31 of the compensator apparatus, the upper sub 33 being connected to the suc-ker rods thereabove. A sufiicient length of polished rod 29 is provided to maintain tension on the rod compensator 27 and to overcome friction of the pump plunger 11 on its downstroke. This assembly is run in the hole on the sucker rod string 12, the pump C being bumped into its seat 98 upon reaching bottom. After the pump has been seated, t-he rod string 12 is spaced out and the polished rod 71 at the top of the hole appropriately hung on the power mechanism D at the top of the hole through the rod rotator mechanism 70 heretofore described, so that when pumping is started, the pump will be tapping bottom very lightly; that is to say, the plunger 11 will be contacting a barrel shoulder 99, or a coupling 100 connected thereto will be tapping the barrel guide 24 lightly. At this time, it may be assumed that the rod compensator 27 is fully telescoped, as disclosed in FIGS. 4, 4a, 4b, the clutch elements 37, 38 being engaged and permitting torque to lbe transmitted through the compensator, if required.

When the pumping operation starts, the tubing string A will elongate as a result of increased hydrostatic pressure therewithin due to the rising column of liquid, and also due to a decreased hydrostatic pressure or head in the annulus surrounding the tubing string, reducing the buoyant effect of the liquid in the well casing on the tubing string A. In addition, the initiation of the pumping operation will increase the average temperature of the tubing string, causing it to elongate, and such increased temperature will also tend to cause the sucker rod string 12 to elongate. However, the rod string may also shorten as a result of the buoyancy of the liquid within the tubing string. The overall net result is that the initial relative spacing of the travelling valve 15, 16 and standing valve 13, 14 of the pump will start changing with the rst stroke of the pump, and will continue changing throughout the life of the well, the changes also being due to the changes in the density of the fluid in the well bore passing through the pump. The plunger 11 may then be located above its desired lowermost position in the barrel 10 at the bottom of its downstroke, as shown in FIGS. 5, 5a.

The rod compensator 27, within the limits of the relative movement that can take place between its housing 50 and mandrel 4l), will automatically compensate for the changing well condition. On the upstroke of the sucker rods 12, the upward force required to lift the fluid in the tubing string is being transmitted from the housing 50 and its sub 36 through the springs 54, cam 52 and locking dogs 45 to the mandrel 40, the parts moving essentially upwardly as a unit to elevate the travelling valve 15, 16 with respect to the standing valve 13, 14. During such upward movement, the clutch 37, 38 (which is only engaged when the rod compensator is fully telescoped, as disclosed in FIGS. 4, 4a, 4b) will be disengaged because of the compressing of the spring 54, and the rod rotator 70 will turn the polished rod 71 and the sucker rods 12, and housing structure 50, connected thereto a partial of a revolution, this turning elort being transmitted through the keys 60 to the clutch dogs 45 to thread the latter a partial revolution around the mandrel 40 and effect a relative upward movement of the housing structure 50 with respect to the mandrel 40 to increase the overall length of the rod compensator, the length of which, for example, may be increased by approximately 0.05 inch. An incremental increase in overall length of the rod compensator 27 occurs on each upstroke of the apparatus, which is accompanied by a turning of the housing structure 50, and the parts within it, relative to the mandrel 40.

The rod compensator will expand or elongate a comparatively short distance on each upward stroke ofthe sucker rods 12, and of the rod compensator 27 and pump C connected thereto. On the downstroke of the sucker rods, rod compensator, and pump, no relative movement between the parts will take place, since they will move downwardly as a unit. The elongation of the rod compensator will continue on each upstroke, the lock dogs 45 being rotated a partial revolution around the mandrel 40, allowing the overall length of the rod compensator to increase by small increments, which, in the example given above, may be 0.05 inch per upstroke. The progressive incremental elongation of the rod compensator actually results in the plunger 11 and its travelling valve 15, 16 occupying a lower position in the barrel on each subsequent downstroke of the pump mechanism until the pump valve rod coupling 100 engages or taps the guide 24, or the plunger taps the shoulder 99 in the pump barrel, as disclosed in FIGS. 6, 6a.

When the tapping commences at the bottom of each stroke of the pump mechanism, downward movement of the mandrel 40 will be arrested. However, the upper housing structure 50 can shift downwardly of the mandrel to a slight extent, this downward shifting being accompanied by a slight downward shifting of the cam 52 from the lock or latch dogs 45, permitting the latter to be expanded by the mandrel thread 43 and shift longitudinally downwardly, or to ratchet downwardly, along the external ratchet thread of the mandrel. Actually, the extent of ratcheting may only be equivalent to a distance between two adjacent thread turns on the mandrel, that might correspond to about or a little greater than 0.05 inch, which is the incremental distance of elongation in the overall length of the rod compensator given above by way of example. Accordingly, the overall length of the rod compensator will be shortened, this shortening being generally equivalent to the amount of its elongation on each upstroke.

On the next upstroke of the sucker rod string 12, including the compensator 27 and the travelling valve 15, 16 of the pump, the rod compensator 27 will again be elongated by virtue of the rotation ofthe sucker rod string, outer housing 50, and mechanism contained therein with respect to the mandrel 40, which is prevented from turning by the square plunger rod 25. On the downstroke, a light tapping of the valve rod coupling 100, or of the plunger 11, will again occur, the portions of the compensator surrounding the mandrel again shifting downwardly therealong, with the latch dogs 45 ratcheting a short distance downwardly along the mandrel thread 43.

As a result of its mode of operation, the rod compensator 27 elongates and contracts, depending on the variable conditions encountered in the well bore. Any excess stroke that will bring the valve rod coupling 100 into contact with the valve rod guide 24 will arrest further downward movement of the mandrel 40 and will result in a downward telescoping of the rod compensator apparatus surrounding the mandrel with respect thereto, to automatically shorten the overall length of the compensator and the effective length of the entire sucker rod string. Assurance is had that' the plunger 11 will be lowered within its companion barrel 1G to the maximum desired extent on each downstroke of the sucker rods 12, insuring a complete upward sweep of the pump barrel by the plunger on its upstroke.

Not only is assurance had that a maximum upstroke of the plunger in the barrel is secured, but the fact that the plunger is shifted downwardly to its lowermost position on each downstroke assures against gas locking, since the bringing of the travelling valve 15, 16 closely adjacent to the standing valve 13, 14 insures sufficient compression of the gas between the two valves as to overcome the hydrostatic head of the fluid in the tubing string A above the travelling valve, effecting opening of the latter and upward passage of gas into the plunger 11. Upon the subsequent upstroke of the plunger, and the upward shifting of the travelling valve 15, 16 away from the standing valve 13, 14, the latter will be opened and additional uid, including gas, if present, will unseat the standing valve element 14 and pass into the barrel 10 thereabove.

The compensator automatically adjusts the position of the plunger 11 to the extent of its merely lightly tapping the barrel. In the example given above, it is only necessary to effect a downward travel of the housing 50 and of the locking mechanism disposed therein along the mandrel of about 0.05 inch to relieve the engaging force of the plunger on the barrel. Such light tapping is insufficient to effect fatiguing of the pumping system and of the sucker rod string 12. This light tapping is to be distinguished from the pounding action that has occurred heretofore when excessive rod lengths were used to cause striking of the plunger mechanism against the barrel.

I claim:

1. In apparatus wherein a pump is disposed in a well bore and is reciprocated by a string of sucker rods for elevating the well production to the top of the well bore, the combination therewith of a compensator forming part of the sucker rod string and comprising an upper device connected to an adjacent sucker rod member and a lower device connected to the pump, said upper and lower devices being shiftable relative to each other, lock means carried by one of said devices and releasably coupled to the other of said devices for transmitting longitudinal m0- tion between said devices to effect operation of said pump, and means responsive to movement of the sucker rod string for effecting shifting of said lock means with respect to said other of said devices to move said devices longitudinally with respect to each other to vary the overall length of said upper and lower devices.

2. In apparatus as dened in claim 1; wherein said means for effecting shifting of said lock means is responsive to turning of said sticker rod string.

3. In apparatus as defined in claim 1; wherein said means for effecting shifting of said lock means is responsive to turning of said sucker rod string, and means at the top of the well bore for turning said sucker rod string.

4. In apparatus wherein a pump is disposed in a well bore, said pump including a standing valve mechanism and a travelling valve mechanism thereabove reciprocated by a string of sucker rods for elevating the well production to the top of the well bore, the combination therewith of a compensator `in the sucker rod string comprising an upper device connected to an adjacent sucker rod member and a lower device connected to the travelling valve mechanism, said upper and lower devices being shiftable relative to each other, lock means carried by one of said devices and releasably coupled to the other of said devices for transmitting motion between said devices to effect reciprocation of said travelling valve mechanism toward and from said standing valve mechanism, and means responsive to movement of the sucker rod string for effecting relative shifting of said lock means along said other of said devices to relatively shift said upper device upwardly along said lower device to increase the overall length of said upper and lower devices and bring the travelling valve mechanism to a bottom position closer to said standing valve mechanism.

5. In apparatus as defined in claim 4; wherein said shifting means effects step-bystep shifting of said lock means along said other of said devices to relatively shift said upper device along said lower device to Aincrease the overall length of said upper and lower devices.

6. In apparatus as defined in claim 4; wherein said lock means is threadedly connected to said other of said devices, said means for effecting relative shifting being responsive to turning of said sucker rod string to relatively thread said lock means along said other of said devices.

7. `l'n apparatus as defined in claim 4; wherein said lock means -is threadedly connected to said other of said devices, said means for effecting relative shifting being responsive to turning of said sucker rod string to relatively thread said lock means along said other of said devices, said threaded connection between said lock means and said other of said devices including ratchet means releasable to effect decrease in the overall length of said upper and lower devices upon lowering of said travelling valve mechanism into contact with said standing valve mechanism.

8. In apparatus as defined in claim 4; and means for effecting shifting of said lower device upwardly of said upper device upon lowering of said travelling valve mechanism into contact with said standing valve mechanism.

9. In apparatus wherein a pump is disposed in a Well bore, said pump including a standing valve mechanism and a travelling valve mechanism thereabove reciprocated by a string of sucker rods for elevating the well production to the top of the well bore, the combination therewith of a compensator in the sucker rod string comprising an outer dev-ice, an inner device telescoped within said outer device, one of said devices being connected to an adjacent sucker rod member, the other of said devices being connected to the travelling valve mechanism, said inner device having an externally threaded portion, lock means carried by said outer device and having an internal threaded portion meshing with said externally threaded portion, means for rotating said sucker rod string and one of said devices relative to said other device to vary the overall length of said inner and outer devices, said internally threaded portion being expandible from threaded mesh with said externally threaded portion to permit non-rotary relative telescoping of said inner device within said outer device to decrease the overall length of said devices.

10. In apparatus as defined in claim 9; wherein said threaded portions are buttress threads.

11. In apparatus as defined in claim 9; said lock means further including a cam engaging said internally threaded portion, and spring means engaging and shifting said lock means longitudinally of said cam to shift said internally threaded portion toward threaded mesh with Said externally threaded portion.

12. In a compensator for varying the eiiective length of a rod string in a well bore: an outer device, an inner device telescoped within said outer device, lock means carried -by one of said devices and lreleasably coupled to the other of said devices for transmitting longitudinal mot-ion between said devices, and means responsive to 10l movement of one of said devices relative to the other of said devices for effecting progressive incremental shifting of said lock means along said other of Said devices to produce step-by-step increase in the overall length of said inner and outer devices.

13. In a compensator as defined in claim 12; wherein said inner device has an externally threaded portion, said lock means having an internally threaded portion meshing with said externally threaded portion, said internally threaded portion being expandible from threaded mesh with said externally threaded portion to permit nonrotary relative telescoping of said inner device within said outer device to decrease the overall length of said devices.

14. In a compensator as defined in claim 12; wherein said inner device has an external buttress thread, said lock means having an internal buttress thread meshing with said external buttress thread, said internally threaded portion of said lock means being expandible from threaded mesh with said external buttress thread to permit nonrotary relative telescoping of said inner device within said outer device to decrease the overall length of said devices.

15. In a compensator as defined in claim 12; wherein said inner device has an externally threaded portion, said lock means having an internally threaded portion meshing with said externally threaded portion, said internally threaded portion being expandible from threaded mesh with said externally threaded portion to permit nonrotary relative telescoping of said inner device within said outer device to decrease the overall length of said devices, said lock means further including a cam engaging said internally threaded portion, and spring means engaging and shifting said internally threaded portion longitudinally of said cam to shift said internally threaded portion toward threaded mesh with said externally threaded portion.

References Cited ROBERT M. WALKER, Primary Examiner, 

1. IN APPARATUS WHEREIN A PUMP IS DISPOSED IN A WELL BORE AND IS RECIPROCATED BY A STRING OF SUCKER RODS FOR ELEVATING THE WELL PRODUCTION TO THE TOP OF THE WELL BORE, THE COMBINATION THEREWITH OF A COMPENSATOR FORMING PART OF THE SUCKER ROD STRING AND COMPRISING AN UPPE DEVICE CONNECTED TO AN ADJACENT SUCKER ROD MEMBER AND A LOWER DEVICE CONNECTED TO THE PUMP, SAID UPPER AND LOWER DEVICES BEING SHIFTABLE RELATIVE TO EACH OTHER, LOCK MEANS CARRIED BY ONE OF SAID DEVICES AND RELEASABLY COUPLED TO THE OTHER OF SAID DEVICES FOR TRANSMITTING LONGITUDINAL MOTION BETWEEN SAID DEVICES TO EFFECT OPERATION OF SAID PUMP, AND MEANS RESPONSIVE TO MOVEMENT OF THE SUCKER 